feat(artifact): add admin APIs for KB consolidation migration

[pinglin]

Because

• The KB consolidation migration (convert000070) needs to move files from legacy/duplicate KBs to the primary default KB
• Files can belong to multiple KBs (many-to-many relationship via junction table)
• After consolidating files, legacy KBs need to be hard-deleted (bypassing soft delete) with CASCADE removal of file-KB associations
• The previous easimon/maximize-build-space action was deprecated

This commit

• Adds AddFilesToKnowledgeBaseAdmin handler that accepts file resource names (namespaces/{namespace}/files/{file}), resolves file IDs to UIDs internally, and inserts into junction table (skipping duplicates via ON CONFLICT DO NOTHING)
• Adds DeleteKnowledgeBaseAdmin handler that drops Milvus collection, purges ACL entry, and hard-deletes KB record (CASCADE removes file_knowledge_base associations)
• Adds HardDeleteKnowledgeBase repository method using Unscoped().Delete() to bypass soft delete
• Adds AddFilesToKnowledgeBase repository method with raw SQL to lookup file UIDs by IDs and insert associations
• Updates integration-test workflow to use jlumbroso/free-disk-space action
• Regenerates repository mocks with new methods